To add to Steve's post, generally you will get a block of IPs where the smallest number is generally the gateway (router's external IP address). What you can do to test this is this:
Get a switch. Plug the router's internal interface into the switch. One of the switch's ports would go to your network as the router did, the other would go to a test box. Enter an IP address one above the router's external IP address using the same subnet mask and the router as the default gateway. So if your router's external IP address is 10.40.192.161, try 10.40.192.162 for your IP address of the test box. Then try to access the internet.
Finally, call your ISP as they should be able to tell you the range. You can also get them to give you the config of the router if they manage it for you as well.
HTH
jocasio
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by: dragon-itPosted on 2006-02-03 at 15:34:08ID: 15869313
They are most likely the block surrounding your external address. Your Netscreen should have an external address and subnet mask. if properly configured that will tell you the block of addresses you have. The router no doubt has the first available in the block.
If you are supposed to have 12 addresses the settings are probably
external ip address xx.xx.xx.xx, subnet mask 255.255.255.240 giving addresses of maybe
xx.xx.xx.0 (unused = subnet)
xx.xx.xx.1 possible router inside address
xx.xx.xx.2 maybe firewall outside address
xx.xx.xx.3
xx.xx.xx.4
xx.xx.xx.5
xx.xx.xx.6
xx.xx.xx.7
xx.xx.xx.8
xx.xx.xx.9
xx.xx.xx.10
xx.xx.xx.11
xx.xx.xx.12
xx.xx.xx.13
xx.xx.xx.14
xx.xx.xx.15 broadcast address
which would give you 12 spare addresses. The range could easily be .16-31, 32-47 etc. too
Either way clearly your ISP will know which addresses are assigned to you.
Steve